Using Selected Options of the Ipconfig Command to Teach Network Troubleshooting Techniques

Journal of Information Systems Education, Fall 2005 by Cavaiani, Thomas P

ABSTRACT

Students often have difficulty troubleshooting common problems that involve network operating system services. Improperly configured network settings can cause unexpected results that add confusion to the troubleshooting process. Commonly used command-line tools may provide students with the information they need to eliminate confusion and provide them with insights for fixing some problems. This teaching tip investigates selected options of the Microsoft Windows ipconfig command and how these options can be used to troubleshoot Active Directory access problems resulting from outdated entries in a local DNS cache.

Keywords: Effective Instruction, Networking, Troubleshooting, Microsoft Windows

1. INTRODUCTION

Becoming proficient at troubleshooting network communications issues is, to say the least, an extremely involved and difficult task. Intensive study of complex technical materials is required just to become superficially familiar with operating systems and networks. Effective instructional techniques typically include hands-on laboratory exercises that provide students with an opportunity to develop a deeper understanding of the processes involved in network communications. To provide such an experience for my students, I have developed a series of lab activities that provide the opportunity to investigate network connectivity as it relates to the TCP/IP protocol stack. Command-line utilities and protocol analyzers are used to provide information regarding the messages sent between client and server during network communications. To illustrate the approach used in these labs, this teaching tip covers an Active Directory lab that my students perform. It demonstrates how selected options of the command-line utility, ipconfig, can provide information to help students analyze network connectivity issues.

2. BACKGROUND

The ipconfig command displays the Internet Protocol (IP) configuration for computers using Microsoft Windows operating systems. IP address, subnet mask, Domain Name System (DNS) addresses, physical addresses, and default gateway addresses are some of the items that are displayed when this command is issued. Ipconfig also supports a number of options for modifying existing configurations. For example, the /release and /renew options are commonly used by administrators to reset IP address information for a given network adapter. The ipconfig command also supports additional options that can be used to reset other existing configurations. One such option is flushdns which can be used to purge entries from the local DNS cache. Operating systems store results of queries to DNS servers in a local cache so that clients do not need to repeatedly query the DNS server for the same address. These DNS cache entries are known as DNS resource records, and the DNS resolver always checks the local cache before it queries the DNS server (DNS Caching, Network Prioritization, and security, 2005).

The default time-to-live (TTL) for most entries in the local DNS resolver cache is 86,400 seconds or 24 hours. Thus a location or service may become inaccessible if an IP address for the service or location changes before the 24 hour period has expired (DNS Caching, Network Prioritization, and security, 2005). Knowing how to rectify this problem is an essential skill for a network administrator. A description of a lab activity designed to guide students through the process of restoring accessibility of certain network services using the displaydns and flushdns options of ipconfig follows.

3. THE LAB ACTIVITY

3.1 Configuring Active Directory Services

The lab activity is designed to provide domain client computers access to Active Directory (AD) services located on a server designated as a domain controller. The lab involves the following three activities: (1) implementation of a domain model, (2) providing access to DNS services, and (3) installation of software on the clients that provides access to AD services.

To implement a domain model, a standalone server is first promoted (converted) to a domain controller using the dcpromo command. This is accomplished by clicking the Start button on the Windows Taskbar, choosing the Run... option, typing dcpromo in the Open text box, and clicking the OK button. A wizard then guides the user through the promotion process, during which the address of an existing DNS server is either specified or DNS software is installed on the server. In this lab, DNS is installed on the domain controller, since no other DNS server is available on the lab network. Upon completion of the promotion process, students modify IP addresses, subnet masks, default gateway, and DNS settings on client computers by manually configured the Internet Protocol (TCP/IP) settings in the Local Area Connection Properties dialog box. Students then join client computers to the domain, by changing the Member of option in the Identification Changes dialog box under Network Identification option in the System Properties dialog box. After restarting their computers students log into the new domain using the domain administrator account, download adminpak.msi from a shared directory on the domain controller, and install it on their client computers so that they can access Active Directory services on the server from their client machines. Finally, students click on the Start button then point to Programs-Administrative ToolsActive Directory Users and Computers to view the Active Directory Users and Computers dialog box that allows them to browse and modify account information (see Figure 1).